Total knee replacement (TKR) has shown increasing success in relieving pain and improving function for patients suffering from knee injury and/or disease. Despite this success, knee implant failure due to wear is still a prominent problem usually leading to revision surgery. Simulators mimicking the motions and loads of knee joints are widely used to evaluate and improve future designs of knee prostheses. However, the input data currently used for simulation is based on typical normal subjects during level walking although there is evidence that more than 75% of patients with a total knee prosthesis walk abnormally. Daily activity levels, realistic knee joint loads and knee motion profiles during these activities, as well as their impact on the wear of the prosthesis for TKR patients are largely unknown. In order to provide accurate input data for preclinical wear testing, we will test the hypothesis that patients with a TKR demonstrate a different motion and load profile during daily physical activities than what is currently used in knee joint simulators. Our preliminary data indicate that in a Swiss TKR population, only 10% of daily activities was spent on "level walking". In addition, the knee joint of these patients most often crossed the 30 degree flexion level, in contrast with the simulator, which crosses the 10 degree level most frequently. This data highlights the discrepancies found between the functional use of the knee joint in the patient's home and community and what is currently used as input data for joint simulators. We will test our hypothesis in TKR subjects who have a Miller-Galante (MG) or Miller-Galante type II (MGII) prosthesis. Subjects will wear an activity monitor for one day which will provide data on their activity level and knee range of motion throughout the day. Subjects will also participate in motion analysis (point cluster technique) which will provide more accurate measurements of the 3-D movement of the knee during these daily activities. Based on the kinematic and kinetic in vivo data derived in the motion laboratory, we will calculate contact forces using a mathematical model of the artificial knee. [unreadable] [unreadable] [unreadable]